After reports swirled that Tyler might be leaving Aerosmith, his unexpected performance with bandmate Perry in New York City on Tuesday night wasn't just a shock to fans but also to Perry. At the performance, Tyler said, "I just want New York to know I'm not leaving Aerosmith."

"I was totally surprised. I had no idea he was going to show up," Perry tells PEOPLE in his first interview since the show. In fact, the pair hadn't spoken in weeks. "All I know is we walked off stage and were sitting taking our break [before] the encore and there was a bunch of commotion and I looked up and Steven was there."

Tyler asked what songs they had left to play, and Perry – who just released a solo album, Have Guitar, Will Travel and was kicking off a tour with his own band, the Joe Perry Project – invited the singer to join him on the Aerosmith classic "Walk This Way."

"I thought I'd be a nice guy and let him sit in," Perry explains. "After 40 years I can say, 'If you want to join in with my band, so much the merrier.'"

After he performed the song, Tyler (who has been recovering from injuries sustained when he fell off the stage over the summer) left without seeing or speaking to Perry again. "He appeared so fast and was gone so fast," says the guitarist, noting that physically, Tyler "seemed fine. He stood up there and sang and that was it."

"Nothing has really changed between two days ago and today," says Perry, who believes that Tyler's intention to take two years off from the band still stands.

But speaking for himself and bandmates Joey Kramer, Brad Whitford, and Tom Hamilton, he adds, "We're still Aerosmith. We don't know what we're gonna do. We've talked about all kinds of different things. Things are still up in the air."

As for whether they will find someone to temporarily replace Tyler, he says, "I can't say right now. We're just getting used to the
idea that he's not going to be available for two years. Anything's possible."